JP2007248139A - Tracking short circuit detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a tracking short circuit occurring in a circuit appropriately in an early stage by excluding variable factors owing to a load instrument. <P>SOLUTION: A peak value of a current waveform passing through the circuit is measured (S1). The standby state of the load instrument is checked on the basis of the measured value of the peak value (S2). In the standby state of the load instrument, the amount of change in the current peak value is calculated (S3). The amount of change is compared to a threshold (S4), and a tracking short circuit is detected when the amount of change exceeds the threshold (S5). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for detecting a tracking short circuit occurring in an electric circuit.

If the power plug is left plugged in for a long period of time, dust, water, moisture, etc. will adhere between the blades of the power plug, creating a carbonized conductive path between the blades and generating a slight spark discharge A phenomenon occurs. Since this phenomenon causes a short circuit between plugs and causes a fire, a method for detecting a tracking short circuit at an early stage is expected.

Conventionally, a method of detecting a tracking short circuit by performing frequency analysis of a current waveform is known. There has also been proposed a method of constantly monitoring the current value of the electric circuit in the operating state of the load device and detecting the occurrence of tracking when the current value exceeds a threshold value (for example, Patent Documents 1 and 2).
Japanese Patent Laid-Open No. 2001-41993 JP 2001-103657 A

However, the method of detecting a tracking short circuit by frequency analysis has a problem that erroneous detection is likely to occur due to variations in detection accuracy. In addition, the method of detecting a tracking short circuit in the operating state of the load device has a large fluctuation in the current waveform due to the usage status of the load device and the inrush current from the load device. It was difficult to distinguish the tracking phenomenon at an early stage.

In order to solve these problems, an object of the present invention is to provide a method capable of accurately detecting a tracking short circuit occurring in an electric circuit at an initial stage by eliminating a variation factor due to a load device.

In order to solve the above problems, the tracking short-circuit detection method of the present invention includes a measurement step of measuring a peak value of a current waveform flowing in an electric circuit, a confirmation step of confirming a standby state of a load device from the measured value of the peak value, and a standby A calculation step for calculating a change amount of a peak value in a state, and a determination step for determining that a tracking short-circuit has occurred when the change amount exceeds a threshold value.

Here, in order to detect the tracking short circuit with higher accuracy, it is preferable to employ the following means.
(A) In the determination step, a multiple of the normal change amount of the peak value in the standby state is used as a threshold value.
(B) In the determination step, it is determined that a tracking short circuit has occurred when the amount of change in the peak value exceeds the threshold value at least twice.
(C) a process in which the calculation step continuously obtains an average value of peak values measured within a predetermined period in a standby state a plurality of times, and a process for obtaining a difference between a maximum average value and a minimum average value among the average values In the determination step, it is determined that a tracking short circuit has occurred when the difference exceeds a threshold value.
(D) A calculation step includes a process of obtaining a maximum value, a minimum value, and an average value of peak values measured within a predetermined period, and a process of obtaining a value obtained by dividing a difference between the maximum value and the minimum value by an average value. In the determination step, it is determined that a tracking short circuit has occurred when the division value exceeds a threshold value.

According to the method of the present invention, since the change of the current peak value is monitored in the standby state of the load device, it is possible to eliminate the fluctuation factor due to the load device and accurately detect the tracking short circuit of the electric circuit at the initial stage. .

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart conceptually showing a tracking short-circuit detection method. The detection method of this embodiment includes a step (S1) of measuring a peak value of a current waveform flowing in an electric circuit, a step (S2) of confirming a standby state of a load device from the measured value of the peak value, and a peak value in the standby state The step includes a step (S3) for calculating the amount of change, a step (S4) for comparing the amount of change with a threshold value, and a step (S5) for detecting a tracking short circuit when the amount of change exceeds the threshold value. . Hereinafter, more specific detection methods will be described in detail with reference to some examples.

FIG. 2 is a flowchart showing Example 1 of the tracking short-circuit detection method, and FIG. 3 (A) is a graph showing a change in current peak value when tracking is not generated in the electric circuit in the standby state of the load device, FIG. 3B is a graph showing changes in the current peak value when tracking occurs in the electric circuit in the standby state.

As shown in FIG. 2, first, the current waveform flowing in the electric circuit is monitored, its peak value is measured, and one measured value is extracted per cycle (S11). Next, based on the measured value of the peak value, it is confirmed whether or not the load device is in a standby state (S12). When the load device is in a standby state, the peak value changes substantially constant, but when the load device is in use, the peak value constantly fluctuates. From this difference, it is confirmed whether the load device is in the standby state or in the use state. When the use state is confirmed, the peak value measurement is continued. When the standby state is confirmed, the process proceeds to the next calculation step.

In the calculation step, the following processing is performed to calculate the amount of change in the peak value in the standby state.
(A) An average value X1 of ten current peak values measured within a period of 10 cycles is obtained (S13).
(B) The same process is repeated six times, and six average values (X1) to (X6) are obtained in a period of 60 cycles (S14).
(C) The maximum average value Xmax and the minimum average value Xmin are obtained from the six average values (X1) to (X6) (S15).
(D) A difference ΔX between the maximum average value Xmax and the minimum average value Xmin is obtained (S16).

Subsequently, the process proceeds to a determination step (S17), where the difference ΔX between the maximum average value Xmax and the minimum average value Xmin is compared with a preset threshold A. Here, when the electric circuit in the standby state is normal, as shown in FIG. 3A, the average values (X1) to (X6) every 10 cycles are almost constant, but tracking is occurring. Sometimes, as shown in FIG. 3B, the average values (X1) to (X6) change greatly. For this reason, the threshold A is set with reference to the amount of change in the current peak value during normal operation, and the threshold A is compared with the difference ΔX obtained by calculation. If the difference ΔX is smaller than the threshold A, it is determined that the electric circuit is normal and the process returns to the measurement step (S11). If the difference ΔX is larger than the threshold A, it is determined that a tracking short circuit has occurred in the electric circuit. (S18).

  According to the detection method of the first embodiment, since the amount of change in the current peak value is monitored in the standby state of the load device, fluctuation factors such as current change due to use of the load device and inrush current from the load device are eliminated. No special data processing is required. For this reason, a tracking short-circuit can be detected with high accuracy at an initial stage by a very simple method, and the occurrence of a fire accident due to the tracking short-circuit can be prevented by operating the circuit breaker according to the detection result. In particular, the average value of the current peak value is obtained within a relatively short 10 cycle period, and tracking is determined based on the difference ΔX of the average value in the 60 cycle period, so that a sudden change in the current waveform that occurs instantaneously is missed. Therefore, it becomes possible to detect a tracking short-circuit continuously with high accuracy.

  FIG. 4 is a flowchart illustrating Example 2 of the tracking short circuit detection method, and FIG. 5 is a graph illustrating a change in the peak value of the current flowing through the electric circuit in the standby state of the load device. The processing of (S21) to (S26) shown in FIG. 4 is the same as the processing of (S11) to (S16) shown in FIG.

  As shown in FIG. 4, the detection method of the second embodiment is different from the first embodiment in the processing for determining tracking. That is, in the second embodiment, a value that is n times the reference value Δα in the standby state is used as the threshold value (Δα × n). Here, the reference value Δα is a value indicating the normal amount of change in the current peak value in the standby state of the load device (the same value as the threshold value A in the first embodiment). For example, as shown in FIG. In the <normal section> in which the amount of change of the value changes substantially constant, it can be obtained from the difference between the maximum average value and the minimum average value of the peak values. The magnification n can be appropriately set according to the type of electric circuit or the detection accuracy of tracking.

Then, the difference ΔX between the maximum average value Xmax and the minimum average value Xmin obtained in the calculation step (S26) is compared with a threshold value (Δα × n) (S27), and when the difference ΔX is smaller than the threshold value (Δα × n). Then, it is determined that the electric circuit is normal, and the process returns to the measurement step (S21). On the other hand, when the difference ΔX exceeds the threshold value (Δα × n), the number of times of excess is subsequently confirmed (S28). For example, if the difference ΔX exceeds only once, this is regarded as noise and the electric circuit is normal. Judge. On the other hand, as shown in FIG. 5, in the <tracking occurrence section> in which the current peak value changes greatly irregularly, if the difference ΔX exceeds the threshold value (Δα × n) several times in succession, It is determined that a tracking short circuit has occurred (S29). Note that the number of times of excess can be set as appropriate according to the type of electrical circuit or the detection accuracy of tracking.

  Therefore, according to the detection method of the second embodiment, since a threshold value that is n times the reference value Δα in the standby state is used in the determination step (S27), a minute current change is erroneously detected as tracking. Less likely. In addition, since tracking is judged when the current peak value difference ΔX exceeds the threshold value (Δα × n) several times in succession, a single waveform change is eliminated as noise, resulting in a continuous waveform change specific to tracking. There is an advantage that it can respond reliably. Furthermore, combining both has the advantage that the detection accuracy can be appropriately selected according to the type and application of the electric circuit. Other effects are the same as those of the first embodiment.

  FIG. 6 is a flowchart showing Example 3 of the tracking short-circuit detection method, and FIG. 7A is a graph showing changes in the current peak value when the electric circuit is normal in the standby state of the load device. B) is a graph showing changes in the current peak value when tracking occurs in the electric circuit in the standby state. The processes of (S31) and (S32) shown in FIG. 6 are the same as the processes of (S11) and (S12) in the first embodiment.

As shown in FIG. 6, the detection method of the third embodiment is different from the first and second embodiments in the process of calculating the change amount of the current peak value in the standby state of the load device. The calculation step of the third embodiment is configured by combining the following processes.
(A) A maximum value, a minimum value, and an average value are obtained from 60 current peak values measured within a period of 60 cycles (S33).
(B) A difference Δ between the maximum value and the minimum value of the current peak value is obtained (S34).
(C) The difference Δ is divided by the average value of the 60 cycle period, and the divided value is obtained as the rate of change Y of the current peak value in the period (S35).

In the subsequent determination step (S36), the rate of change Y is compared with a preset threshold value B. Here, when the electric circuit in the standby state is normal, as shown in FIG. 7A, the average values (X1) to (X3) in the 60 cycle period are almost constant, but tracking is occurring. Sometimes, as shown in FIG. 7B, the average values (X1) to (X3) change greatly. For this reason, the threshold value B is set based on the rate of change of the current peak value in the normal state, and the threshold value B is compared with the rate of change Y obtained by calculation. If the rate of change Y is smaller than the threshold value B, it is determined that the electric circuit is normal and the process returns to the measurement step (S31). If the rate of change Y exceeds the threshold value B, a tracking short circuit has occurred in the electric circuit. (S36).

  Even in the detection method of the third embodiment, since the amount of change in the current peak value is monitored in the standby state of the load device as in the first embodiment, the variation factor due to the use of the load device is eliminated, and a very simple method is used. A tracking short circuit can be detected with high accuracy at an initial stage. In particular, since the amount of change in the current peak value is calculated as the rate of change Y every 60 cycle periods, the change in the current waveform can be monitored with a margin over a relatively long period, and a minute current change or single current can be monitored. The possibility of erroneously responding to changes can be reduced, and the reliability of tracking detection accuracy can be increased. In the detection method of the third embodiment, the same determination method as that of the second embodiment is adopted, and a value that is a multiple of the normal change rate is used as the threshold value B, and the change rate Y obtained by calculation sets the threshold value B to the threshold value B. It can also be configured to determine tracking when it exceeds several times in a row.

2 is a flowchart of a tracking detection method conceptually showing an embodiment of the present invention. It is a flowchart of the tracking detection method which shows Example 1 of this invention. 4 is a graph illustrating a change in current peak value in order to supplementarily explain the detection method of Example 1. FIG. It is a flowchart of the tracking detection method which shows Example 2 of this invention. 6 is a graph illustrating a change in current peak value in order to supplementarily explain the detection method of Example 2. It is a flowchart of the tracking detection method which shows Example 3 of this invention. 10 is a graph illustrating a change in current peak value in order to supplementally explain the detection method of Example 3.

Explanation of symbols

S1 Step for measuring peak value S2 Step for checking standby state S3 Step for calculating change amount of peak value S4 Step for comparing change amount with threshold S5 Step for detecting tracking short circuit

Claims (5)

A method of detecting a tracking short circuit occurring in an electric circuit,
A measurement step for measuring the peak value of the current waveform flowing in the electric circuit;
Confirmation step to confirm the standby state of the load device from the measured value of the peak value,
A calculation step for calculating a change amount of the peak value in the standby state;
A determination step of determining that a tracking short-circuit has occurred when the amount of change exceeds a threshold;
A method of detecting a tracking short circuit, comprising: The tracking short-circuit detection method according to claim 1, wherein in the determination step, a multiple of a normal change amount of the peak value in the standby state is used as a threshold value. The tracking short-circuit detection method according to claim 1, wherein in the determination step, it is determined that a tracking short-circuit has occurred when a change amount of the peak value exceeds the threshold value at least twice. The calculation step includes a process of continuously obtaining an average value of peak values measured within a predetermined period in a standby state a plurality of times, and a process of obtaining a difference between a maximum average value and a minimum average value among the average values,
The tracking short-circuit detection method according to any one of claims 1 to 3, wherein in the determination step, it is determined that a tracking short-circuit has occurred when the difference exceeds a threshold value. The calculation step includes a process of obtaining a maximum value, a minimum value, and an average value of peak values measured within a predetermined period, and a process of obtaining a value obtained by dividing a difference between the maximum value and the minimum value by an average value,
The tracking short circuit detection method according to any one of claims 1 to 3, wherein in the determination step, it is determined that a tracking short circuit has occurred when the division value exceeds a threshold value.

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